Single piece hub with integral upper and lower female cones and method for making the same

ABSTRACT

To simplify fabrication of an integral hub piece, the opening between the upper and lower female cones in this hub has sufficient width or radial dimension to allow access to both cones from one side of the hub with the cutting tool. A cutting tool is used which has a width smaller than the opening between the cones. Preferably, the tool has a width which is about equal to or smaller than an angular dimension through this opening which is defined by extending surfaces of the upper and lower female cones. If this limitation is satisfied, both cones can be created with a single machine set up operating from one side of the integrated hub. Preferably the tool should only move orthogonal or parallel to the cutting tools rotational center axis.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims priority to provisional application Ser. No.60/138,945, filed Jun. 11, 1999.

FIELD OF THE INVENTION

The present invention relates to the field of fluid dynamic bearings,and more specifically to a process for accurately cutting the conicalsurfaces into a hub to define the hub faces for a conical bearing, sothat the motor hub is designed as a single component.

BACKGROUND OF THE INVENTION

Fluid dynamic bearings have come into increasingly wide-spread use,especially in fields where the stability of the shaft and bearingassembly is of critical importance, such as in the field of disk drivesand the like. Ball bearing assemblies have many mechanical problems suchas wear, run-out and manufacturing difficulties. Moreover, resistance tooperating shock and vibration is poor because of flow damping. Thus,fluid dynamic bearings where in a lubricating fluid such as gas orliquid or air provides a bearing surface between a fixed member of thehousing and a relatively rotating member have come into increasinglywide-spread use. Such fluid dynamic bearings spread the bearing surfaceover a large continuous area in comparison with the ball bearingassembly which comprises a series of point interfaces. This is desirablebecause the increased bearing surfaces reduce wobble or run-out betweenthe rotating and fixed members. Further, improved shock resistance andreadiness is achieved with a fluid dynamic bearing. Also, the use offluid in the interface area imparts damping effects to the bearing.

An especially desirable design is a conical bearing, as a single bearingor a pair of facing bearings can impart substantial radial and axialstability to a system.

However, due to nominal gaps in a conical fluid bearing on the order of1 to 3 microns, precise size and positional control must be maintainedduring component fabrication and assembly. If not done, the assembledcomponents will not have the proper geometric relationships necessary toproduce a functional air bearing when the parts rotate at the operatingspeed.

SUMMARY OF THE INVENTION

For purposes of this description, a dual conical fluid bearing spindleincludes four basic components. These components are the upper malecone/shaft, the upper female cone, the lower male cone/shaft and thelower female cone. According to the present invention, the upper andlower female cones are integrated into a single part, more specificallythe hub. This hub, in designs of a disk drive or the like where theshaft is fixed, may support an external flange for supporting one ormore disks for rotation with the hub.

To simplify fabrication of this integral hub piece, the opening betweenthe upper and lower female cones in this hub has sufficient width orradial dimension to allow access to both cones from one side of the hubwith the cutting tool. A cutting tool is used which has a width smallerthan the opening between the cones. Preferably, the tool has a widthwhich is about equal to or smaller than an angular dimension throughthis opening which is defined by extending surfaces of the upper andlower female cones. If this limitation is satisfied, both cones can becreated with a single machine set up operating from one side of theintegrated hub.

Preferably the tool should only move orthogonal or parallel to thecutting tools rotational center axis.

This assembly design and fabrication technique eliminates the toleranceaccumulation associated with the assembly of separate upper and lowerfemale cones. Further, since the component manufacturing operation isdone on the same machine set-up, there will be no error associated withrechucking the hub between two separate fabrication operations.

Other features and advantages of the present invention will becomeapparent to a person of skill in the art who studies the followinginvention disclosure given in association with the following set ofdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are exploded views of the basic components of a dualcone fluid dynamic bearing;

FIG. 2 is a modified version of FIG. 1 showing in this instance theintegrated upper and lower female cones which are a subject of thepresent invention;

FIG. 3 is a vertical section of the integrated hub comprising the upperand lower female cones and with the essential dimensions of the presentinvention illustrated;

FIG. 4 is a vertical sectional view similar to the view of FIG. 3illustrating the cutting tool, the width of the opening, and the widthof the tool which is used to cut both the upper and lower conesaccording to the present invention;

FIG. 5 is a modified version of FIG. 4 showing cutting of the lower coneof the integrated cones; and

FIG. 6 shows the integrated hub comprising the upper and lower femalecones, the upper male shaft/cone and the lower male shaft/cone allintegrated into an exemplary motor in which the fluid dynamic bearing isuseful.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A typical conical fluid bearing spindle has the basic parts shown inFIG. 1A comprising an upper male cone/shaft element 10, an upper femalecone 12, a lower male cone/shaft element 14 and a lower female cone 16.Typically, each of these pieces is separately fabricated. The pieces canthen be assembled by joining the upper and lower female cones 12, 16.The shaft 22 of the upper male cone/shaft 10 is then inserted into thebore 24 of the lower male cone/shaft 14. Prior to doing this, of course,the upper female cone 12 and lower female cone 16 must be joinedtogether, perfectly aligned. A further alternative appears in FIG. 1Bwhere the male cones slide over or are otherwise fitted on a shaft whichis inserted through the openings 65 in the cone sections 12, 16 whichare joined as above. Due to the nominal gaps in a conical fluid bearingbeing on the order of 1 to 3 microns, precise size and positionalcontrol must be maintained during component fabrication and assembly. Ifnot, the assembled components will not have the proper geometricrelationships necessary to produce a bearing when the parts rotate atoperating speed. Fabrication technology does exist to manufacture eachof the individual components of FIGS. 1A and 1B to a high degree ofprecision. However, it is evident that to improve the positional controlof the components in the assembly, that it would be highly desirable toproduce an integrated hub 50 as shown in FIG. 2. This integrated hubwould include both the upper and lower female cones 52, 54, respectivelyintegrated into a single part.

The successful final machining process for this single piece hub 50shown in its rough cast or machined form in FIG. 3 relies primarily ontwo dimensions marked as 60 and 62 in FIG. 3. Dimension 60 is the radialwidth of the opening 65 between the upper and lower female cones;dimension 62 is the angular width of the opening, which may be definedas the distance between two lines which extend from inner surfaces ofthe cone. The dimension 60 is set large enough to allow the shaft of thecombination cones/shaft 10, FIG. 2 to pass through the opening 60. Inthe present example, the shaft 22 is shown attached to the cone 23;obviously, the shaft could equally well be attached to the lowercones/shaft 14 with the bore 24 appearing in the upper male cones/shaft10. In a further alternative, the dimension 60 could be set large enoughto allow for joinder of two mating surfaces of an upper and lower malecone 41, 43 as in FIGS. 1A and 1B. However, such an approach is moredifficult to assemble accurately and stabilize as the two pieces must bejoined inside the integral hub 50.

The critical dimension is the dimension 62 which is the dimensiondefined at the center line 65 of the opening between the upper 67 andlower 66 cone openings in the integral hub piece 50. The dimension 62 isdefined and extends between a first line 70 drawn colinear with theconical surface of the upper cone and a second line 74 drawn parallel toline 70 and colinear with the conical surface of the lower hub femalecone 76.

The significance of this dimension 62 becomes apparent from a comparisonof FIGS. 4 and 5 which show the use of an exemplary tool for cutting onthe surfaces 52,54 of the upper and lower cones 67,66. This tool 90mounted on a support shaft 92 is designed to have a width 94 which isless than (or about equal to) the dimension 62 (FIG. 3) defined by theopening between the two surfaces 72, 76 (FIG. 3). It is evident from acomparison of the figures that the dimension 94, which represents thewidth of the tool, must be less than or about equal to the dimension 62which is the angular width of the opening defined by the lines 70, 74extending parallel to selected parallel surfaces of the upper and lowercones. In this way, the tool 90 may first cut the surface 52 of theupper cone, and then be pushed through the opening 65 to cut the surface54 of the lower cone 66. By adopting this approach, access to both cones66, 67 from one side of the hub is achieved. With a cutting tool 90having a dimension 94 less than the critical angular opening dimension62, both female cones 66,67 defined by their surfaces 52,54 can becreated with a single machine set-up. This assembly design andfabrication technique eliminates the tolerance accumulation associatedwith the assembly of separate upper and lower female cones into a singlehub with a single unitary hub being substituted. Furthermore, since thecomponent manufacturing operation is done in a single machine set-up,there is no error associated with rechucking the hub between twoseparate fabrication operations. Therefore, the highly precisedimensions of the cones can be achieved. Finally, either the part beingcut, or the cutting tool can move in forming the female conicalsurfaces.

This approach using a single unitary hub can be used to establish eithera rotating hub, rotating about a fixed shaft, or a fixed hub with arotating shaft. For example, referring back to FIG. 2, it can be seenthat hub 50 of FIG. 2 includes a disk support ledge 100, so that the hubas it rotates about the integrated shaft 10, 14 can support one or moredisks for rotation. In contrast, in FIG. 6 a complete motor is shownincorporating the unitary hub 50 of the present invention with aextended portion 110 of the hub supporting a magnet 112 which cooperateswith a stator 114 to drive a motor. The same external portion 110 of thehub 50 rotates within a recess in base 120 which may be incorporatedinto a disc drive or the like. A disc support surface can be provided onthe hub.

Other features and advantages of the present invention may becomeapparent to a person of skill in the art who studies this disclosure.Therefore, the scope of the invention is to be limited only by thefollowing claims.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. A method of forming anintegral, one piece hub for a dual conical fluid dynamic bearingcomprising: defining a center hole having an opening dimensioned toaccommodate a narrow end of each cone of a dual conical bearing, as wellas passage of a tool for cutting surfaces of each of a pair of femalecones in said hub defining each of a pair of female cones in saidintegral hub utilizing the tool which has a width dimension less than orequal to the angled dimension through the central opening so that eachof said pair of female cones may be cut from one side of said hub.
 5. Amethod as claimed in claim 4 in which the hole is dimensioned toaccommodate the tool passing from one of the cones to the other of thecones without substantially changing the angle of the tool relative to acentral axis of the integral hub.
 6. A method as claimed in claim 5wherein a maximum dimension for the tool is defined by drawing a lineover a projected finished surface for each of said cones through thehole through which the tool passes, the distance between the linesestablishing a maximum width of the tool.
 7. A method as claimed inclaim 6 wherein the distance between the lines is established at thecenter hole of the integrated hub.
 8. A dual conical fluid dynamicbearing comprising a hub having first and second female cones definedtherein and joined by a central opening, the central opening being asufficient width to accommodate means for serially cutting the first andsecond cones without modification of setup of said hub relative to saidcutting means.
 9. A fluid dynamic bearing as in claim 8 wherein saidmeans for cutting cuts said conical surfaces serially.
 10. A motor hubfor use in a dual conical fluid dynamic bearing comprising first andsecond conical elements joined together with their narrow ends facingeach other, the motor hub comprising first and second female openingsdefined by generally conical surfaces and joined together at an openingnear the center of the hub, the opening between the first and secondcones being sufficiently large to allow a tool traversing on a coneangle through the central opening to define both first and secondconical surfaces on a single machine set up.
 11. A motor hub as claimedin claim 10 wherein the hub opening is axially thin enough that thenarrow ends of the conical elements can be directly formed together.